Analog control system

ABSTRACT

A feedback control system for use in connection with automatic material-handling apparatus for controlling the acceleration and/or deceleration curve of a movable material-handling assembly, as for example, an automatic or semiautomatic robot used in conjunction with delivering and retrieving material from a storage warehouse, wherein the distance from a fixed or variably selectable point is sensed and utilized to generate a speed curve for controlling the incremental variation in speed of the material-handling apparatus up to a preselected maximum speed or down to zero speed.

United States Patent Griner [S4] ANALOG CONTROL SYSTEM 8/1970 Hall et al. ..3l8/611 [72] Inventor: Ralph R. Gnner, Mount Clemens, MlCh. Primay Examiner-Arthur L La Point [73] Assignee: Palmer-Shile Company, Detroit, Mich. A i t Examiner-George H, Libman [22] Filed: July 3, 1969 AttorneyHarness, Dickey & Pierce [21] Appl. No.: 838,767 [57] ABSTRACT A feedback control system for use in connection with auto- U-S- Cl- A, B matic materiabhandling apparatus for controlling the ac. II.-

eleration and/or deceleration curve of a movable material. [58] Field of Search ..214/16.42; 246/182 B, 187 B handling assembly as for example, an automatic or Semiauto matic robot used in conjunction with delivering and retrieving [56] (defences cued material from a storage warehouse, wherein the distance from UNITED STATES PATENTS a fixed or variably selectable point is sensed and utilized to generate a speed curve for controlling the incremental varia- 3,318,260 5/1967 Gillespie ..246/187 X tion in Speed f the materiaphandling apparatus up to a S P 'ITY at preselected maximum speed or down to zero speed. ml! 3,519,805 7/1970 Thome-Booth ..246/182 B X 71 Claims, 21 Drawing Figures 1 2 5%,? 4 Hy] View 2231; I 710? /35 W if f y 4 (H197; 5/ 661/ e g/l ar 1,7 7011/71 0778 F2641 17 3 J wwrferl/ W Z Mi #4 14/4 j/fi Jree l Opera/e 7rm 6/ [01/21/61 1 /Z4[ 1 724}. Fax/7M4 p f pf firdi yci frat a! /jZ /p 7 x a 401412 65 pa i f :5 62221712 67 1/ 5c 1 L 4 if lcfccfor g g0 -K Zara S E Tram :7 \s ji; /7J zf /fi & 8E )iefr'reru'e j E Yera 1751667 i Fix n71 /%4f2z Frrzmye! 71am! //7? a 71170 I Inf flea I figff L445 4 64/25 L 7 1/; we

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SHEET 1% OF 18 INVENTOR. 5%? i 5/727! PATENTED FEB 1 B72 SHEET ISUF 18 ANALOG CONTROL SYSTEM BACKGROUND AND SUMMARY OF THE DEVELOPMENT This invention relates generally to acceleration and/or deceleration, feedback, control system for a driving motor, and more particularly to acceleration and/or deceleration characteristic control system utilizing an internally generated acceleration or deceleration curve signal which is particularly adapted to utilize, in conjunction with the automatic or semiautomatic material-handling systems, the acceleration or deceleration curve being generated in accordance with a speed-versus-distance function.

In material-handling systems which incorporate a conveying device, as for example, a robot for handling palletized loads, it is desirable to operate the material-handling device at as great a speed as is practical to progress from one station to another station or a position adjacent another station. Subsequently, the system is devised to accelerate and decelerate the material-handling device as rapidly as possible consistent with accurately positioning the material-handling device at the preselected stopping point and preventing undue horizontal forces on the material being handled.

Automated material-handling machines are in common use in many processing industries, as for example, in the automatic warehousing industries. These machines are particularly adapted to automatically transfer palletized loads from an input station to a preselected address station which corresponds to a particular bay within the storage complex. Further, the automatic transfer system must elevate the palletized load to a preselected level within the bay, deposit the load at that level. The automatic transfer mechanism may have been given a second command, or may be given a second command at that time, to subsequently pick up a second load at a different station and deliver the second load to a conveying apparatus for pickup. Thus, the automatic transfer mechanism must accelerate the load with the capability of being able to decelerate and accurately stop at the second pickup address. Thereafter, the transfer mechanism will accelerate toward a home station and finally follow a deceleration cycle to stop at the home station and deposit the load. The system of the present invention is described in conjunction with an automatic robot type of material handling which is adapted to be utilized in an automatic warehousing complex. However, it is to be understood that other material-handling systems may utilize principles of the present invention, as for example, systems which are adapted to transfer workpieces to a successive number of processing stations.

In certain areas of the material-handling control art, systems have been utilized to control acceleration and deceleration (dv/dt) using a feedback signal from a tachometer, for the speed-sensing type, to control the system. Thus, the system is controlled in response to a speed-versus-time relationship. Certain other systems have been evolved which utilize a relatively complex hydraulic motor control system which must be very precisely controlled and/or predicted to anticipate the inherent mechanical and hydraulic inertia of the system. Thus, it is necessary to predict the response time of the various elements of the system, for example, the hydraulic portion of the system, in order to accurately position the work-handling assembly relative to the final position desired.

In accordance with the system of the present invention, an electrical analog feedback control has been devised which utilizes the principle of controlling the speed of a materialhandiing apparatus in response to a speed-versusdistance relationship. Specifically, a continuously operating pulse generator and coder assembly, such as a Baldwin precision shaft position encoder, may be utilized to generate output pulses in direct response to and directly driven by the drive wheels or other precision responsive portion of the materialhandling apparatus. The continuously generated pulses are generally not utilized during the fullspeed operation of the system, i.e., when the system is not in the acceleration,

deceleration or pretravel mode of operation. However, when it is determined that the position of the equipment requires an acceleration or deceleration mode of operation, an acceleration or deceleration curve is generated in response to the gating of the pickup device for the encoder. The energization of the pickup may be accomplished substantially instantaneously due to its electrical characteristics, and the sensed pulses are utilized as a measure of distance traveled by the robot.

The output from the pickoff, once energized, appears as a series of pulses, the number of pulses being a fixed constant for linear distance of travel of the material-handling assembly, in the order of approximately 2,000 pulses per revolution of the wheel in the Baldwin encoder or approximately 32 pulses per linear inch of travel. These pulses are fed into a counter which controls a digital-to-analog converter system, the output of which varies in accordance with a preselected function of the number of input pulses. This output is utilized to control the motor driving the particular material-handling assembly being controlled.

Generally automatic systems of the type referred to in this application, by way of example, generally comprise a carrier or automatic robot which is movable along a trackway, the trackway being disposed adjacent to and parallel with the open side of a storage frame. The storage frame defines storage racks or bins on which palletized material loads may be stored. A carriage is mounted on the carrier or automatic robot and is adapted to be vertically movable relative to the track and storage frame and the carriage is provided with a work-handling platform or forks for transferring a load laterally between the carriage and the storage frame at preselected ones of the racks or bins. The carrier may be disposed in an aisle between two storage frames with the platform or a pair of forks being insertable into either storage frame, either by turning of the carriage or by symmetrical movement of the platform in either lateral direction.

The carrier preferably has a home position or input station which may, for example, be located at one end of the aisle. The input station is conveniently located for loading and unloading the carrier and may serve as a reference point from which the carrier, carriage and platform or forks start in a sequence of movement designated to deposit a load in a storage frame, retrieve a load from the storage frame or transfer loads within the system. The system could further be extended to perform any other series of movements required to the operation of a material storage system. However, in the system to be described in conjunction with the present invention, the home position is not utilized as the reference point from which the carrier operates. Rather, a series of coded indicia blocks are supplied along the frame, which indicia blocks are sensed by the traveling carrier to determine at what particular location the carrier is passing at any particular time. It is the coded blocks which are utilized to start the acceleration or deceleration cycle rather than the generation of a position signal relative to the home station.

To carry out the above sequence of movements or commands, the carrier is provided with a means for storing and carrying out the commands such as a signal storage and readout of programming system, wherein coded commands may be stored in an electronic or magnetic storage register or other like storage device in a receiver carried by the carrier, which said coded commands are read out to effect the desired sequential movement. In the particular system to be described, 35 bit commands are used to describe the storage or retrieval operations to be performed.

In the system of the present invention, the commands are transferred from the computer to the fixed command console which is mounted adjacent the home station. The commands are then transferred to the automatic robot through an optical, magnetic, or other type of through air" systems. The commands given to the robot are stored within the robot and utilized in its travel down the aisle to the selected coded address, as sensed from the coded blocks mounted on the frame. The racks are provided with the series of coded address tabs as 

1. In a material-handling apparatus for delivering material from one point to another including a carrier and a motor for driving the carrier, the improvement comprising a control system for controlling the acceleration and/or deceleration of the carrier comprising signal-generating means for generating a signal representative of a motion during at least a selected period of time, controlled conducting means transmitting said signal during a portion of said at least a selected period of time, and function generator means for generating a speed-versus-distance acceleration and/or deceleration curve in response to said transmitted signal for controlling the speed of the motor, said function generator including digital storage means for storing a digital binary number representative of a speed characteristic of the motor and providing an output signal for said speed control, the speed varying in response to the magnitude of the binary number, and means altering said binary number aS a function of the distance traveled by the carrier after the start of the portion of the time to vary the speed of the carrier in accordance with the altered number.
 2. The improvement of claim 1 wherein said storage means includes a presettable counter.
 3. The improvement of claim 2 wherein said digital binary number is set into said counter at least as early as the start of said portion of time.
 4. The improvement of claim 3 further including a digital-to-analog converter and wherein the output of said counter is used to control the speed of the carrier.
 5. The improvement of claim 4 wherein said control system further includes a summing circuit and a speed-biasing circuit, the output of said converter and said biasing circuit being fed to said summing circuit, the output of the summing circuit controlling the carrier.
 6. The improvement of claim 5 wherein said converter provides a predetermined speed signal to said summing circuit which may be reduced to zero, said biasing circuit producing, when said speed signal is zero, an additional speed signal to control the speed of said carrier.
 7. The improvement of claim 6 wherein said biasing circuit signal is a fixed presettable signal, said biasing signal operating the carrier at a low creep speed.
 8. The improvement of claim 7 wherein said speed-biasing circuit includes a creep speed reference circuit which is presettable with a digital binary signal, said speed-biasing circuit further including a digital-to-analog comparator for inverting said creep speed reference signal.
 9. The improvement of claim 8 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a stroking cylinder feedback assembly, and means for comparing the output of said stroking cylinder feedback assembly with said speed signal for fixing the speed of the hydraulic driver for a given speed signal.
 10. The improvement of claim 9 wherein the control system further includes an analog comparator and said stroking cylinder feedback assembly provides an analog signal representative of the speed of the hydraulic driver, said analog comparator comparing the analog speed signal from said analog-summing circuit and the analog signal for said stroking cylinder feedback assembly to achieve a coincidence.
 11. The improvement of claim 1 wherein said digital storage means is a presettable decrementable counter for generating a deceleration curve in response to the altering of the binary number in accordance with distance traveled.
 12. The improvement of claim 1 wherein said digital storage means is a presettable incrementable counter for generating an acceleration curve in response to the altering of the binary number in accordance with the distance traveled.
 13. The improvement of claim 1 wherein said altering means includes a comparator circuit, said comparator circuit being sequentially provided with a series of numbers which vary in accordance with the variation of said binary number said comparator circuit varying said binary number upon achievement of a preselected relationship between said binary number and a function of distance traveled by the carrier.
 14. The improvement of claim 13 wherein said control system further includes a distance-signal generating circuit for generating an output signal which varies as a function of distance traveled by the carrier.
 15. The improvement of claim 14 wherein the generation of the distance-traveled signal to said comparator circuit commences at least as late as the start of said portion of the selected period of time.
 16. The improvement of claim 14 wherein said control system further includes a distance tachometer which generates a series of pulses, the number of pulses generated being a function of distance traveled.
 17. The improvement of claim 16 wherein said control system further includes gating means disposed between said tachometer and said travel comparator, said gating means being controlled to provide the output pulses from said tachomeTer at least as late as the start of said period.
 18. The improvement of claim 17 further including counting means interconnected with said tachometer to count at least certain of said output pulses from said tachometer.
 19. The improvement of claim 18 wherein counting means counts all of the pulses during the period that said deceleration curve is being generated.
 20. The improvement of claim 19 wherein the binary number set into said decrementable counter is fed to said comparator and the output from said tachometer pulse counting circuit is also fed to said comparator, and means for generating an output signal from said comparator when coincidence is achieved between the binary number and the tach pulses counted by said counting circuit.
 21. The improvement of claim 20 wherein said output signal is fed to said decrementable counter and said tach counter circuit, said output signal resetting said counter circuit.
 22. The improvement of claim 21 wherein said output signal decrements said decrementable counter.
 23. The improvement of claim 22 wherein said analog signal is decreased in response to the decrementing of said decrementable counter.
 24. The improvement of claim 23 wherein said decrementable counter is decremented to a count of zero.
 25. The improvement of claim 24 wherein said storage means includes a presettable counter.
 26. The improvement of claim 25 wherein said digital binary number is set into said counter at least as early as the start of said portion.
 27. The improvement of claim 26 further including a digital-to-analog converter and wherein the output of said counter is used to control the speed of the carriage.
 28. The improvement of claim 27 wherein said control system further includes a summing circuit and a speed-biasing circuit, the output of said converter and said biasing circuit being fed to said summing circuit, the output of the summing circuit controlling the carrier.
 29. The improvement of claim 28 wherein the output of said decrementable counter is fed to the input circuit of said digital-to-analog converter, said converter providing a zero output signal when said counter has been decremented to zero.
 30. The improvement of claim 29 wherein said speed-biasing circuit provides an additional signal to said summing circuit to maintain said carrier at a creep speed.
 31. The improvement of claim 30 wherein said speed-biasing circuit includes a creep speed reference circuit which is presettable with a digital binary signal, said speed-biasing circuit further including a digital-to-analog converter for converting said creep speed reference signal.
 32. The improvement of claim 31 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a stroking cylinder feedback assembly, and means for comparing the output of said stroking cylinder feedback assembly with said speed signal for fixing the speed of the hydraulic driver for a given speed signal from said summing circuit.
 33. The improvement of claim 32 wherein the control system further includes an analog comparator and said stroking cylinder feedback assembly provides an analog signal representative of the speed of the hydraulic driver, said analog comparator comparing the analog speed signal from said analog-summing circuit and the analog signal for said stroking cylinder feedback assembly to achieve a coincidence.
 34. The improvement of claim 31 further including means for sensing a preselected position of said carrier relative to one of said one or another stations, numbers for generating a position signal in response to sensing of said position, and means for terminating said creep speed reference signal in response to said signal.
 35. The improvement of claim 34 further including means for sensing the decrementing of said decrementable counter to zero, said gating means being controlled to cease transmission of pulses from said tachometer pulse counting circuit in response to decrementing said counter to zero.
 36. The improvement of claim 35 further including pulse detector means for sensing the generation of pulses from said tachometer generator, said pulse detector circuit generating an output signal in response to a preselected characteristic of said tachometer generator output.
 37. The improvement of claim 36 wherein said preselected characteristic is the lack of a pulse from said tachometer generator for a preset period of time.
 38. The improvement of claim 37 wherein said pulse detector circuit includes means for sensing when said tach pulse generator switches from the generation of a pulse to the lack of generation of a pulse, said circuit providing an output signal when said tach pulse generator fails to switch from the generation of a pulse for a preselected period of time.
 39. In a material-handling apparatus for delivering material from one station to another including a material carrier and a motor for driving the carrier, the improvement comprising a method of controlling the acceleration and/or deceleration of the carrier comprising generating a signal representative of a motion during at least a selected period of time, transmitting said signal during a portion of said at least a selected period of time, and generating a speed-versus-distance acceleration and/or deceleration curve in response to said transmitted signal for controlling the speed of the motor, including storing a digital binary number representative of a speed characteristic of the motor, generating an output signal for said speed control, the speed varying in response to the magnitude of the binary number, and altering said binary number as a function of the distance travelled by the carrier after the start of the portion of the time to vary the speed of the carrier in accordance with the altered number.
 40. The method of claim 39 further including storing said binary number at least as early as the start of said portion.
 41. The method of claim 40 further including using the output said of said counter to control the speed of the carriage.
 42. The method of claim 41 further including providing a predetermined speed signal to a summing circuit which may be reduced to zero, and also providing a biasing signal, when said speed signal is zero, as an additional speed signal to control the speed of said carrier to operate said carrier at a presettable, fixed, low creep speed.
 43. The method of claim 42 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a stroking cylinder feedback assembly, and the method further including comparing the output of said stroking cylinder feedback assembly with said speed signal for fixing the speed of the hydraulic driver for a given speed signal.
 44. The method of claim 43 wherein the method further includes providing an analog signal representative of the speed of the hydraulic driver, and comparing the analog speed signal and the analog signal for said stroking cylinder feedback assembly to achieve a coincidence.
 45. The method of claim 39 further including providing with a series of numbers which vary in accordance with the variation of said binary number, and varying said binary number upon achievement of a preselected relationship between said binary number and a function of distance travelled by the carrier.
 46. The method of claim 45 further including generating an output signal which varies as a function of distance travelled by the carrier.
 47. The method claim 46 further including commencing the distance-traveled signal at least as late as the start of said portion of the selected period of time.
 48. The method of claim 47 further including the step of generating a series of digital pulses as a function of distance traveled.
 49. The method of claim 48 further including the step of controlling the transmission of said pulses during said portion, the start of said transmission of said pulses being at least as late as the start of said period.
 50. The method of claim 49 further including The step of counting the pulses generated during said period and comparing said counted pulses with said stored binary number and generating an output signal when coincidence is achieved between the count of said pulses and said binary number.
 51. The improvement of claim 50 wherein said binary number is decremented in response to achievement of coincidence.
 52. The method of claim 51 wherein said binary number is decremented to a count of zero.
 53. The improvement of claim 52 wherein said zero binary number provides a zero speed signal to said carrier, and the method further including providing an additional speed signal to said carrier to operate said carrier at a creep speed.
 54. The method of claim 53 wherein the claim is a hydraulically driven robot, the hydraulic driver including a stroking cylinder feedback assembly including means for generating a signal as a function of the setting of said stroking cylinder, the method further including the step of comparing the signal from the output of the stroking cylinder with the speed signal, including said additional signal, for fixing the speed of the hydraulic driver for a given speed signal.
 55. In a material-handling apparatus for delivering material from one point to another including a carrier and a motor for driving the carrier, the improvement comprising a control system for controlling the acceleration of the carrier comprising signal-generating means for generating a signal representative of a motion during at least a selected period of time, controlled conducting means transmitting said signal during a portion of said at least a selected period of time, and function generator means for generating a speed-versus-distance acceleration curve in response to said transmitted signal for controlling the speed of the motor, said function generator including storage means for storing a number representative of a speed characteristic of the motor and providing an output signal for said speed control, the speed varying in response to the magnitude of the number, and means altering said number as a function of the distance traveled by the carrier after the start of the portion of the time to vary the speed of the carrier in accordance with the altered number, a pretraveling portion preceding said deceleration curve, said pretravel portion being a linear distance of travel of the carrier, the control system including speed control means for controlling the carrier during both the pretravel portion and the deceleration curve, a travel comparator circuit, pulse-generating means for generating a series of pulses in response to distance traveled by the carrier, and a pretravel counting circuit for counting the pulses generated by said tach generating means, said travel comparator comparing a preset digital number with the pulses counted by the travel counter circuit and terminating the pretravel portion when coincidence is achieved between said preset number and the count of the counter circuit.
 56. The improvement of claim 55 wherein said pretravel counting circuitry includes a count divider and a travel counter said count divider dividing the pulses from said tach generating means.
 57. The improvement of claim 56 wherein said travel counter counts the output pulses from said count divider.
 58. The improvement of claim 57 wherein said travel counter provides a digital binary input coded signal to said travel comparator circuit said travel comparator circuit comparing the output of said travel counter with said preset digital number.
 59. The improvement of claim 58 wherein said control circuit includes a first and second pretravel digital storage circuit, said first pretravel storage circuit storing a large number relative to said second pretravel digital storage circuit.
 60. The improvement of claim 59 wherein said first pretravel storage circuit stores a number which provides the said travel comparator with a digital number causing a greater pretravel distance than said second pretravel storage circuIt.
 61. The improvement of claim 60 wherein coincidence in said travel comparator generates a pretravel complete output signal.
 62. The improvement of claim 61 wherein said pretravel complete signal routes said tach pulses directly to said travel counter.
 63. The improvement of claim 62 wherein the control system further includes a presettable digital speed reference counter and said pretravel complete signal presents the output of said speed reference counter to said travel comparator to initiate the start of the deceleration portion of the cycle.
 64. The improvement of claim 7 wherein said speed-biasing circuit includes a creep speed reference circuit which is presettable with a creep speed reference signal.
 65. The improvement of claim 64 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a feedback assembly, and means for comparing the output of said feedback assembly with said speed signal for fixing the speed of the hydraulic driver for a given speed signal.
 66. The improvement of claim 65 wherein the control system further includes an comparator and said feedback assembly provides a signal representative of the speed of the hydraulic driver, said comparator comparing the speed signal and the signal from said feedback assembly to achieve a coincidence.
 67. The improvement of claim 31 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a feedback assembly, and means for comparing the output of said feedback assembly with said speed signal for fixing the speed of the hydraulic driver or a given speed signal.
 68. The improvement of claim 67 wherein the control system further includes a comparator and said feedback assembly provides a signal representative of the speed of the hydraulic driver, said comparator comparing the speed signal and the signal for said feedback assembly to achieve a coincidence.
 69. The method of claim 42 wherein the carrier is a hydraulically driven robot, the hydraulic driver including a feedback assembly, and the method further including comparing the output of said feedback assembly with said speed signal for fixing the speed of the hydraulic driver for a given speed signal.
 70. The method of claim 69 wherein the method further includes providing a signal representative of the speed of the hydraulic driver, and comparing the speed signal and the signal for said feedback assembly to achieve a coincidence.
 71. The method of claim 53 wherein the claim is a hydraulically driven robot, the hydraulic driver including a feedback assembly including means for generating a signal as a function of the setting of said feedback assembly, the method further including the step of comparing the signal from the output of the feedback assembly with the speed signal, including said additional signal, for fixing the speed of the hydraulic driver for a given speed signal. 